Radio controlled model airplanes are normally started with a hand-held motor with a driver rubber bushing on the end of the shaft. Holding onto the plane with one hand, the rubber bushing or cup is pressed with the other hand against the propeller spinner, thereby turning over the engine to start it.
In this process, the person's face is directly over the propeller, which is made from wood or plastic. If breakage should occur, the operator would be in great danger of injury. Further, when the engine starts, adjustment of the throttle valve is done by reaching around the moving propeller, placing the arm at some risk. Also, glow-plug engines need to have a battery to supply the voltage to the glow plug. Here again, the operator must reach around the moving propeller to remove the battery after starting. These propellers spin at speeds of 8,000 to 25,000 RPM. The engine's power is from a fraction of a horsepower to 3 Hp and higher. The starting of the engine procedure can be a high-risk injury situation.